The sleep of healthy male and female subjects between the ages of 50-70 is being assessed. The structure of sleep is being measured by four nights of laboratory electroencephalographic recordings, the patterns of sleep by two week home sleep diaries and the subjective aspects by nightly post sleep reports and questionnaires. The measures are to be related to an extensive battery of cognitive-personality measures. Subpopulation of retired 60-70 year old subjects and a nurse population who had had extensive shift work schedules in their early careers are beeng studied.